A fuel cell is a power generation device for taking out electrical energy by electrochemically oxidizing fuel such as hydrogen and methanol. The fuel cell has been attracting attentions of the world these days as a clean energy source. The fuel cell can be classified depending on the type of the electrolyte into a phosphoric-acid type, a fused carbonate type, a solid oxide type, a solid polyelectrolyte type, etc. Of these, the polymer electrolyte fuel cell is a type of fuel cell that generates electricity by supply hydrogen on one side and oxygen on the other side of a membrane electrode assembly having electrodes arranged on both sides of an electrolyte membrane. As the polymer electrolyte fuel cell can generate a power density equivalent to that of an internal combustion engine, it has been widely researched in order to achieve its practical application as a power source for electric vehicles.
In a polymer electrolyte fuel cell, a unit cell generally is formed by sandwiching a solid polymer electrolyte membrane with a hydrogen side electrode and an oxide side electrode. A plurality of such unit cells are laminated via a separator, to form a fuel cell stack. A gas diffusion layer, which is a porous member with electric conductivity, is generally provided between the electrode and the separator. The gas diffusion layer serves to stably transfer hydrogen, oxygen, water, electron, heat, etc., between an electrode layer and an external circuitry.
Dry-out or flooding can be a cause of making operation of a fuel cell instable. The dry-out means a malfunction of a fuel cell wherein electrical resistance of electrolyte membrane increases under dry conditions of a fuel cell to induce instability of the fuel cell. The flooding means a malfunction of a fuel cell wherein gas passage is blocked due to liquid water generated under moistness conditions of a fuel cell to induce instability of the fuel cell.
As a means of improving anti-flooding properties, a gas diffusion layer has been known which is produced by coating its surface with a porous conductive fine particle layer comprising carbon and polytetrafuluoroethylene attached to the carbon (refer to Patent Document 1).